Screen cleaning device



July 19, 1966 G. M. DICK 3,261,468

SCREEN CLEANING DEVICE Filed May 17, 1963 4 Sheets-Sheet 1 FIG.

I IL 26 I ||l IIll| IHI l. ll h July 19, 1966 G. M. DICK SCREEN CLEANINGDEVICE 4 Sheets-Sheet 2 Filed May 17, 1963 FIG. 5

July 19, 1966 mcK 3,261,468

SCREEN CLEANING DEVICE Filed May 17. 1963 4 Sheets-Sheet 3 F IG. 4 I

July 19, 1966 e. M. DICK SCREEN CLEANING DEVICE 4 Sheets-Sheet 4.

Filed May 17, 1963 United States Patent .0

3,261,468 SCREEN CLEANING DEVICE George M. Dick, Sherbrooke, Quebec,Canada, assignor to Bird Machine Company, South Walpole, Mass., acorporation of Massachusetts Filed May 17, 1963, Ser. No. 281,297 7Claims. (Cl. 209-243) This invention relates to fibrous pulp screeningapparatus and more particularly to an improved screen cleaning devicefor such processing apparatus.

It has previously been proposed to employ a screen cleaning device orfoils mounted for movement in a circular path across the face ofcylindrical screens to maintain the screens free from obstruction.However, for optimum effectiveness, the clearance between the foils andthe screen surface must be quite small and must be maintained uniformalong the axis of the screen. This small and uniform clearance hasrequired additional support and reinforcement for the foils, a conditionwhich has tended to decrease the effectiveness of the foils because ofthe additional turbulence produced in the pulp by movement of thereinforcement therethrough. In addition, such support and reinforcementhas presented surfaces against which occasional long strings of fiberhave tended to accumulate, forming clumps which produce still furtherturbulence and power loss.

It is the general object of the present invention to avoid and overcomethe foregoing and other difficulties of and objections to prior artpractices by the provision of an improved screen cleaning device whicheliminates the accumulation of deleterious fibrous bundles and stringsin the annular chamber or fiber passageway adjacent the screen orscreens of the fibrous pulp screening apparatus; prevents jamming of thescreen cleaning device against the screen or screens; prevents cloggingof the screen or screens; and permits the fibrous pulp screeningapparatus to be operated by a low horsepower drive means.

Another object of the present invention is to provide an improved screencleaning device which provides uniform pulsing on the adjacent screenalong the length of a cleaning foil.

Yet another object of the present invention is to provide an improvedscreen cleaning device which provides improved direction of undesirablematerial in the stock toward the reject trap.

Still another object of the present invention is to provide an improvedscreen cleaning device which provides improved direction of undesirablematerial in the stock from the adjacent screen.

The aforesaid objects of the present invention, and other objects whichwill become apparent as the description proceeds, are achieved byproviding, in one embodiment of the invention, a screening device forfibrous pulp having a generally cylindrical screen and means forconducting a stream of pulp across a cylindrical face of said screen, animproved screen cleaning device comprising at least one elongated foilsupported adjacent one end only thereof for movement in a circular pathabout the axis of the screen and across a face thereof, the clearancebetween the foil and the adjacent screen face varying from the supportedend to the free end of the foil at rest, the extent of said variation atrest being substantially equal to the extent of bending of said foilunder the influence of centrifugal force under operating conditions, andmeans for rotating said foil about said axis to clean said screen.

The objects of the invention are-achieved in another embodiment of theinvention by providing a screen cleaning device in which at least oneelongated foil is provided which is supported adjacent one end onlythereof for movement in a circular path about the axis of the screen3,261,468 Patented July 19, 1966 and across a face thereof, the foilbeing hollow and filled with air or other gas so as to have minimum massand consequently to be subject to so little stress under the influenceof centrifugal force during operation that no appreciable bendingoccurs; consequently, the hollow foil is mounted so that the clearancebetween the foil and screen face is uniform along the length of the foilat rest and remains so during operation.

For a better understanding of the present invention, reference should behad to the accompanying drawings, wherein like numerals of referenceindicate similar parts throughout the several views and wherein:

FIG. 1 is a side elevational view partially in vertical section of afibrous pulp screening apparatus of the general type shown in US. PatentNo. 2,975,899 incorporating the improved screen cleaning device of thepresent invention; 1

FIG. 2 is an enlarged plan view of the spider taken along the line 2-2of FIG. 1 in the direction of the arrows;

FIG. 3 is a side elevational view partly broken away along the line 33of FIG. 2 in the direction of the arrows showing a foil mounting lug formounting an outer foil;

FIG. 4 is a view partly in vertical section along the line 4-4 of FIG. 3in the direction of the arrows;

FIG. 5 is a view along the line 55 of FIG. 2 in the direction of thearrows;

FIG. 6 is a view partly in vertical section along the line 6-6 of FIG. 5in the direction of the arrows;

FIG. 7 is a diagrammatic side elevational view of an inclined straightfoil disposed adjacent the inner surface of a screen;

FIG. 8 is a view similar to FIG. 7 of an inclined straight foil disposedadjacent the outer surface of a screen;

FIG. 9 is a view similar to FIG. 7 of a variant in which the screen hasa conical face and the foil lies in a true cylindrical surface when atrest;

FIG. 10 is a side elevational view of a helical foil for improveddirection of undesirable material in the stock toward the reject trap;

FIG. 11 is a fragmentary view in horizontal section of an outer foil ofunique cross-sectional configuration for directing undesirable materialin the stock away from the screen;

FIG. 12 is a fragmentary view in horizontal section of an inner foil ofunique cross-sectional configuration for directing undesirable materialin the stock away from the screen;

FIG. 13 is a fragmentary view corresponding to FIG. 1 showing anotherembodiment of the invention; and

FIG. 14 is a view in section taken along line 14-14 of FIG. 13.

Although the principles of the present invention are broadly applicableto all types of fibrous pulp screening apparatus, the present inventionis particularly adapted for use in conjunction with apparatus forscreening paper pulp and hence it has been so illustrated and will be sodescribed.

With specific reference to the form of the present invention illustratedin the drawings, and referring particularly to FIG. 1, a paper pulpscreening apparatus of the general type shown in US. Patent No.2,975,899 is indicated by the reference numeral 10.

This paper pulp screening apparatus 10 comprises an in ner cylindricalscreen 12 and outer cylindrical screen 14-, concentrically spaced fromeach other. Inlet means 16 introduces a stream of liquid suspensionunder pressure into the top of the annular chamber or fiber passageway18 defined by the inner screen 12 and outer screen 14. A screen cleaningdevice such as a pair of inner vanes or foils 20 (FIG. 6) and a pair ofouter foils 22 of the present invention are mounted on rotatable foilmounting means, such as a rotatable spider 24, for rotational movementadjacent the inner screen 12 and outer screen 14. Drive means 26 forrotating a spider shaft 28, the spider 24, and the inner foils 20 andouter foils 22 comprises the V-belt pulley 30, connected by conventionalmeans, such as belts 32, to a conventional source of power, such as anelectric motor (not shown).

It will be understood that the outer foils 22 are disposed adjacent theinner face of the outer screen 14 and that the inner foils 20 aredisposed adjacent the outer face of the inner screen 12. All of thefoils, upon rotation of spider 24, are mounted for movement in acircular path about the axis of the screens and across their faces.

The liquid suspension passes through the inner screen 12 and outerscreen 14 into an inner annular chamber 34 and outer annular chamber 36,respectively, and thence into delivery means 38 for withdrawing screenedliquid suspension from the inner annular chamber 34 and outer annularchamber 36. Reject means 40 accepts rejected material from the fiberpassageway 18.

As shown in FIGS. 1 and 2, in order to facilitate removal of the screencleaning device, the spider 24 has an inner circular mounting plate 42connected by bolts 44 (FIG. 2) to an outer ring 46 having a pluralityof, for example, two inner foil mounting lugs 48 (FIGS. 2, 5, and 6),and two outer foil mounting lugs 50 (FIGS. 2-6) depending therefrom.

Mounting of inclined outer foils 22 Referring to FIG. 4, an outer foil22 is mounted at an angle B with respect to the axis of rotation of thespider 24 by means of shims 52 disposed between the outer foil 22 andouter foil mounting lug 50. Bolts 54 and a key 56 on the outer foil 22projecting into a keyway 58 in the outer foil mounting lug 50 secure theouter foil 22 at the desired angle B with respect to the axis ofrotation.

It will be understood by those skilled in the art that the outer foil 22may be also mounted at an angle B with respect to the axis of rotationwithout the necessity of using shims by appropriate tapering of thecontact surfaces 60, 62 of the lug or foil respectively. As a result ofthe angular mounting of the foils, the clearance between each foil andthe adjacent screen surface, when the foil is at rest, is not uniformbut varies along the length of the foil, increasing toward the free endof the foil. This variation is substantially equal to the extent ofdistortion or bending of the foil under the influence of centrifugalforce under operating conditions, i.e., when the foils are swept acrossthe faces of the screens by rotation of spider 24 to clean the screensof any accumulated pulp.

Further, so that undesirable material in the stock may be directed awayfrom the screen, such as outer screen 14 (FIG. 11) or inner screen 12(FIG. 12) when rotation is in the direction of the arrows, faces 662 and660 respectively arranged at an angle with respect to the screensurfaces may be provided on outer foil 220 and inner foil 200.

Mounting 0f inclined inner foils As shown in FIG. 6, an inner foil 20may be similarly mounted at an angle B with respect to the axis ofrotation of the spider 24 by the use of shims 552, bolts 542, key 562,and keyway 582. In the case of the inner foils, the variation inclearance decreases toward the free end of each foil.

The angles B and B may be calculated readily in any particular case bycomputing the centrifugal force under intended operating conditions andthe deflection caused by the force for given materials of constructionand dimensions. The centrifugal force F in pounds is computed asfollows:

where W=weight of the foil in pounds N :revolutions per minute R=radiusof rotation in feet g:32.2

If for example:

The deflection S in inches of the free end of the foil is computed asfollows:

=398 lbs.

If for example:

B =04. The angle B or B of course, is a function of S and L.

Operation As shown in FIG. 7 the outer foil 22 disposed at the angle Bwith respect to the axis of rotation is rotated at a speed suflicient toproduce an area of reduced pressure between the outer screen 14 and theouter foil 22, the outer foil 22 has moved from the solid line positionshown in FIG. 7 to the dotted line position shown in such figuresubstantially parallel to the axis of rotation, thus providing normalpulsing along the entire length of the outer screen 14.

Reference to FIG. 8 will indicate that the inner foil 20 operates in asimilar manner with respect to the inner screen 12.

For the purpose of more efficiently directly undesirable material in thestock toward the reject trap, an inclined foil, such as an inner foil 20(FIG. 10), may he formed as a portion of a helix having a steep pitchangle a with respect to the axis of rotation.

It will also be understood that the desired results can be obtained byemploying a screen, the face of which is part of a conical surface, incombination with conventional foils which themselves lie in a truecylindrical surface when at rest, provided that the angle between thescreen and the foil is as set forth above, as shown in FIG. 9 for thecase of the outer foil.

It will be apparent from the foregoing that when the mass of the foil isreduced by constructing it of a low density material such as aluminum,titanium, or a nonmetallic synthetic plastic or by making the foil ofhollow construction, the magnitude of angle B or B may be reduced.Indeed, in the case of hollow foils, the mass of the foil may be reducedto the point where angle B or B may be zero for all practical purposes.In the embodiment shown in FIGS. 13 and 14, outer foil 250 is hollow,being made from sheet metal, e.g., austenitic stainless steel, andhermetically sealed so that it contains only air or other gas. The lowmass of foil 250 so reduces stress on the foil due to centrifugal forceduring operation that no appreciable bending of the foil occurs and theclearance between the foil and the screen remains substantially uniformboth when the foil is at rest and when it is in operation.

It will be recognized by those skilled in the art that the objects ofthe present invention have been achieved by providing an improved screencleaning device which eliminates the accumulation of deleterious fibrousbundles and strings in the fiber passageway adjacent the screen of afibrous pulp screening apparatus, prevents jamming of the screencleaning device against the screen, prevents clogging of the screen, andpermits the operation of the fibrous pulp screening apparatus by a lowhorsepower drive means. Further, the improved screen cleaning deviceprovides uniform pulsing on the adjacent screen. In addition, suchimproved screen cleaning device provides improved direction ofundesirable material in the stock both toward the reject trap and awayfrom the screen.

While in accordance with the patent statutes preferred and alternativeembodiments of the present invention have been illustrated and describedin detail, it is to be particularly understood that the invention is notlimited thereto or thereby.

What is claimed is:

1. In a screening device for fibrous pulp having a generally cylindricalscreen, and means for conducting a stream of pulp across a face of saidscreen, an improved screen cleaning device comprising at least oneelongated foil, means for supporting said foil adjacent one end only formovement in a circular path about the axis of the screen and across aface thereof and spaced from said face, the clearance between the foiland the adjacent screen face varying from the supported end to the freeend of the foil at rest, the extent of said variation at rest beingsubstantially equal to the extent of bending of said foil under theinfluence of centrifugal force under operating conditions, so that underoperating conditions, the clearance between said foil and said screen issubstantially uniform, and: means for rotating said foil about said axisto clean said screen.

2. A screening device as claimed in claim 1 in which said foil is ofhelical configuration.

3. A screening device as claimed in claim 2 in which said foil ismounted for movement across the inner face of said screen and theclearance increases toward the free end.

4. A screening device as claimed in claim 2 in which said foil ismounted for movement across the outer face of said screen and theclearance decreases toward the free end.

5. A screening device as claimed in claim 1 in which said screen isexactly cylindrical.

6. A screening device as claimed in claim 1 in which said screen atleast in part has a slightly conical surface.

7. In a screening device for fibrous pulp having a generally cylindricalscreen and means for conducting a stream of pulp across a face of saidscreen, an improved screen cleaning device comprising at least oneelongated foil supportedadjacent one end only for movement in a circularpath about the axis of the screen and across a face thereof, theclearance between the foil and the adjacent screen face being uniformalong the length of the foil at rest, said foil being hollow andhermetically sealed and containing essentially only a gaseous fluid inits interior to minimize its mass and the extent of bending of said foilunder the influence of centrifugal force under operating conditions, andmeans for rotating said foil about said axis to clean said screen.

References Cited by the Examiner UNITED STATES PATENTS 439,700 11/ 1890Stevens 210-374 641,773 1/ 1900 Hoeschen 233-7 2,204,349 6/ 1940F-orrest 210-415 2,247,605 7/ 1941 Casagrande 210-374 2,796,809 6/1957Sprau 209-306 2,868,500 1/1959 Boulet 253-39.15 2,975,899 3/1961 Cannon209-273 FOREIGN PATENTS 28,226 1 1/ 1906 Austria. 24,801 2/ 1883Germany. 822,325 10/ 1951 Germany. 773,742 5/ 1957 Great Britain.

HARRY B. THORNTON, Primary Examiner.

R. HALPER, Assistant Examiner.

1. IN A SCEENING DEVICE FOR FIBROUS PULP HAVING A GENERALLY CYLINDRICALSCREEN, AND MEANS FOR CONDUCTING A STREAM OF PULP ACROSS A FACE OF SAIDSCREEN, AN IMPROVED SCREEN CLEANING DEVICE COMPRISING AT LEAST ONEELONGATED FOIL, MEANS FOR SUPPORTING SAID FOIL ADJACENT ONE END ONLY FORMOVEMENT IN A CIRCULAR PATH ABOUT THE AXIS OF THE SCREEN AND ACROSS AFACE THEREOF AND SPACED FROM SAID FRAME, THE CLEARANCE BETWEEN THE FOILAND THE ADJACENT SCREEN FACE VARYING FROM THE SUPPORT END TO THE FREEEND OF THE FOIL AT REST, THE EXTENT OF SAID VARIATION AT REST BEINGSUBSTANTIALLY EQUAL TO THE EXTENT OF BENDING OF SAID FOIL UNDER THEINFLUENCE OF CENTRIFUGAL FORCE UNDER OPERATING CONDITIONS, SO THAT UNDEROPER-